linux-kernel - Re: [RESEND PATCH 3/3] x86/apic: Clean up the names of legacy irq mode setting related functions

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Date:   Fri, 19 Jan 2018 15:21:30 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
        hpa@...or.com, x86@...nel.org, rostedt@...dmis.org,
        jgross@...e.com, peterz@...radead.org, uobergfe@...hat.com,
        joro@...tes.org
Subject: Re: [RESEND PATCH 3/3] x86/apic: Clean up the names of legacy irq
 mode setting related functions

On 01/19/18 at 02:42pm, Dou Liyang wrote:
> Hi Baoquan,
> 
> At 01/05/2018 12:39 PM, Baoquan He wrote:
> [...]
> >   /*
> > - * Not an __init, needed by kexec/kdump code.
> > - * For safety IO-APIC and Local APIC need be cleared before this.
> > + * In legacy irq mode, full DOS compatibility with the uniprocessor PC/AT is
> > + * provided by using the APICs in conjunction with standard 8259A-equivalent
> > + * programmable interrupt controllers (PICs). It's necessary to deliver legacy
> > + * interrupts even when APIC mode is not enabled. This is required by kexec/
> > + * kdump before enter into the 2nd kernel.
> >    */
> >   void switch_to_legacy_irq_mode(void)
> >   {
> >   	if (!nr_legacy_irqs())
> >   		return;
> > -	x86_io_apic_ops.disable();
> > +	ioapic_set_virtual_wire_mode();
> > +
> > +	if (boot_cpu_has(X86_FEATURE_APIC) || apic_from_smp_config())
> > +		lapic_set_legacy_irq_mode(ioapic_i8259.pin != -1);
> 
> Seems these two function, ioapic/lapic_set_legacy_irq_mode should be
> exclusive.

Thanks for looking into this, dou!

It might be not exclusive. You can see mp_spec 3.6.2.2 Virtual Wire Mode
subsection, there are two kinds of virtual wire mode, one is
8259A-Equivalent pics is connected to lint0 of boot cpu LAPIC, the other
is 8259A-Equivalent pics go through IO-APIC, then is connected to lint0
of LAPIC. Whatever it is, LAPIC need be set as through-lapic.

Above is what I got from mp_spec. But from function
native_disable_io_apic() and disconnect_bsp_APIC(), the code seems to be
telling that if io-apic is connected to 8259A-Equivalent pics, we need
mask lvt0 of LAPIC. This conflicts with mp_spec 3.6.2.2.

Thanks
Baoquan
> 
> But We do that because both the through-lapic and through-ioapic virtual
> wire mode need setup the APIC_SPIV_APIC_ENABLED which is only located in
> the lapic_set_legacy_irq_mode(). So we need call them both.
> 
> IMO, this cleanup may not make it clear. we can separate these two mode
> totally or just keep it like before.
> 
> Thanks,
> 	dou.
> >   }
> >   #ifdef CONFIG_X86_32
> > diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
> > index 1151ccd72ce9..c30f0f273dbd 100644
> > --- a/arch/x86/kernel/x86_init.c
> > +++ b/arch/x86/kernel/x86_init.c
> > @@ -148,5 +148,5 @@ void arch_restore_msi_irqs(struct pci_dev *dev)
> >   struct x86_io_apic_ops x86_io_apic_ops __ro_after_init = {
> >   	.read			= native_io_apic_read,
> > -	.disable		= native_disable_io_apic,
> > +	.disable		= switch_to_legacy_irq_mode,
> >   };
> > diff --git a/drivers/iommu/irq_remapping.c b/drivers/iommu/irq_remapping.c
> > index 49721b4e1975..751472ddf536 100644
> > --- a/drivers/iommu/irq_remapping.c
> > +++ b/drivers/iommu/irq_remapping.c
> > @@ -37,7 +37,7 @@ static void irq_remapping_disable_io_apic(void)
> >   	 * now.
> >   	 */
> >   	if (boot_cpu_has(X86_FEATURE_APIC) || apic_from_smp_config())
> > -		disconnect_bsp_APIC(0);
> > +		lapic_set_legacy_irq_mode(0);
> >   }
> >   static void __init irq_remapping_modify_x86_ops(void)
> > 
> 
>